As officials haggle over emission targets and a long-term strategy to address climate change this week in Montreal, glaciological experts have warned of 'Himalayan tsunamis' caused by outbursts of mountain lakes swollen by snow melt.

At a recent international workshop here, scientists agreed global warming was now a certainty and it was already bringing dramatic changes to snow cover in the Himalaya.

'Projections indicate that the magnitude and frequency of flashfloods in the greater Himalayan region may increase in the future as a result of change in climate and its variability,' said the Lhasa Declaration issued at the end of the conference that was sponsored by the Kathmandu-based ICIMOD and the China Meteorological Administration.

ICIMOD already has a regional flood initiative for exchanging hydrological data but says Himalayan flashfloods need even greater crossborder cooperation because many of the steep rivers flow across boundaries and reaction time is measured in hours, not days.

"Major Himalayan rivers are transboundary river basins and flashfloods will not respect national borders," says Xu Jianchu, a Chinese scientist with ICIMOD, "that is why we need to think regionally and act locally."

Indeed, an existing bilateral early warning mechanism between India and China prevented what could have been a catastrophe on the Sutlej River in February this year. By the time flood waters surged through Himachal Pradesh, people had been evacuated and no lives were lost.

Similarly, despite strained relations between India and Pakistan they share warning through radio broadcasts and this prevented another potentially devastating loss of life on the Chenab earlier this year.

However, officials say a lot more needs to be done to map hazardous valleys, glacial lakes in Bhutan, Nepal and Tibet that are in danger of bursting and to transmit rainfall data in real time so downstream regions have time to evacuate.

"There is a lack of exchange of real time data and there needs to be a regional mechanism for this," says Mandira Shrestha, a water resource specialist at ICIMOD.

Although Nepal has got the most experience in the region in mapping and draining glacial lakes, our domestic warning system for big rainfall events is almost non-existent which is why flashfloods triggered by cloudbursts in the central midhills during monsoons in 1981, 1993, 2002 and 2003 were so catastrophic.

"There is no operational flood-forecasting in Nepal," says Arun Bhakta Shrestha of the Department of Hyrdology and Meteorology..

Pradeep Mool of ICIMOD is an international expert on glacial lake outburst floods (GLOFs) and says there is now little doubt that climate variability is causing rapid glacial retreat, especially in the eastern Himalaya. The frequency and damage caused by GLOFs have been increasing due to climate change, and Mool is working with Chinese scientists to study several lakes in Tibet that drain into the Trisuli and Bhote Kosi that are in danger of bursting.

The Bhote Kosi Power Company has installed sensors all the way up to the Chinese border that gives the 46 MW project five minutes warning in case of a GLOF. There are 42 glacial lakes in the Bhote Kosi basin in Tibet and the river has a history of flashfloods. "What we'd like is to have sensors further upstream and extend the warning time," says Bhote Kosi's Sandip Shah.

There have been 25 glacial lake floods recorded in Nepal and more than half of them originated in Tibet. Of the 2,315 glacial lakes within Nepal, 20 are said to be extremely dangerous. And one only needs to look at geological evidence of past events to see the kind of damage they can cause. Pokhara is situated on the debris field of a catastrophic flashflood on the Seti some 800 years ago which if it happened today could cause up to 200,000 deaths.

Average temperatures across the mountains are increasing at 0.06 degrees a year. Glacial lakes that used to be small ponds 20 years ago are now 5 sq km and larger.

Closer cooperation between China and Nepal could protect downstream infatructure and towns in Nepal not just in the Bhote Kosi but the Trisuli and Arun as well. Says ICIMOD Director General J Gabriel Campbell: "We must make information travel faster than flashfloods."

Himalayan Tsunamis ROBIN MCKIE

Nawa Jigtar was working in the village of Ghat in Manang when the sound of crashing sent him rushing out of his house. He emerged to see his herd of cattle being swept away by a wall of water. Jigtar and his fellow villagers were able to scramble to safety. They were lucky: "If it had come at night, none of us would have survived."

Ghat was destroyed when a lake, high in the Annapurnas, burst its banks. Swollen with glacier melt its walls of rock and ice had suddenly disintegrated. Several million cubic metres of water crashed down the mountain. When Ghat was destroyed in 1985 such incidents were rare. Not any more.

Last week, scientists revealed that there has been a tenfold jump in such catastrophes in the past two decades, the result of global warming. Himalayan glacier lakes are filling up with more and more melted ice and 24 of them are now poised to burst their banks in Bhutan, with a similar number at risk in Nepal.

But that is just the beginning, a report in Nature said. Future disasters around the Himalaya will include floods, droughts, land erosion, biodiversity loss and changes in rainfall and the monsoon. The roof of the world is changing, as can be seen by Nepal's Khumbu glacier, where Hillary and Tenzing began their 1953 Everest expedition. It has retreated 5 km since their ascent. Almost 95 percent of Himalayan glaciers are also shrinking and that kind of ice loss has profound implications, not just for Nepal and Bhutan but for surrounding nations, including China, India and Pakistan.

Eventually, the Himalayan glaciers will shrink so much their meltwaters will dry up, say scientists. At the same time, rivers fed by these melted glaciers, such as the Indus, Yellow and Mekong, will turn to trickles in the dry season. Drinking and irrigation water will disappear. Hundreds of millions of people will be affected.

"There is a short-term danger of too much water coming out of the Himalayas and a greater long-term danger of there not being enough," says Dr Phil Porter of the University of Hertfordshire. "Either way, it is easy to pinpoint the cause: global warming."

According to Nature, temperatures in the region have increased by more than 1 C recently and are set to rise by a further 1.2C by 2050, and by 3C by the end of the century. This heating has already caused 24 of Bhutan's glacial lakes to reach 'potentially dangerous' status, according to government officials. Nepal is similarly affected.

"A glacier lake catastrophe happened once in a decade 50 years ago," said UK geologist John Reynolds, whose company advises Nepal. "Five years ago, they were happening every three years. By 2010, a glacial lake catastrophe will happen every year."

An example of the impact is provided by Luggye Tsho, in Bhutan, which burst its banks in 1994, sweeping 10 million cubic metres of water down the mountain. It struck Panukha, 50 miles away, killing 21 people. Now a nearby lake, below the Thorthormi glacier, is in imminent danger of bursting. That could release 50 million cubic metres of water, a flood reaching to northern India 150 miles downstream.

Not only villages are under threat: Nepal and Bhutan have built hydroelectric plants selling electricity to India and these could be destroyed in coming years. Worse, when Nepal's glaciers melt, there could be no water to drive run-of-the-river plants. A Greenpeace report last month suggested that the region is already experiencing serious loss of vegetation.